Toolholder having a clamping arm and a spacer for preventing overclamping

ABSTRACT

A toolholder for holding a cutting insert, particularly for grooving and/or parting operations. The toolholder comprises a base and a clamping arm forming therebetween a pocket and a slot. The pocket is open at a front end thereof for receiving the cutting insert, and the slot extends rearwardly from a rear end of the pocket. A fastening screw extends through the slot from the clamping arm to the base for displacing the clamping arm toward the base in order to clamp the cutting insert within the pocket. A spacer is disposed in the slot for limiting an extent of movement of the clamping arm toward the base, thereby preventing overclamping of the clamping arm.

RELATED INVENTION

This application is related to an invention disclosed in the inventors'concurrently filed U.S. application Ser. No. 09/151,097 filed Sep. 10,1998 U.S. Pat. No. 6,010,281 (Attorney Docket No. 024444-533).

FIELD OF THE INVENTION

The present invention relates to a toolholder for chip removingmachining, preferably for grooving or parting, and a method of attachinga cutting insert in a toolholder.

PRIOR ART

In U.S. Pat. No. 3,844,008 a tool of the above mentioned type isdescribed. A clamp is activated by a screw for clamping the cuttinginsert in an insert pocket. Often when the screw is tightened theoperator over-torques or over-tightens the screw such that the clampundergoes a plastic deformation. The plastic deformation of the clampleads to a less accurate clamping for the next insert to be used sincethe clamp has been distorted.

In Soviet Application No. A1-1720803 there is shown a tool for mountinga self-wedging insert wherein the minimum height of the insert pocketfor accuracy reasons is determined by means of an adjustable threadedsleeve. In practice, an insert is inserted into an insert pocket formedbetween a base and a clamping arm. A fastener screw is then rotated tofix the insert in place. Then, the sleeve is rotated and caused to moveupwardly through the base and into engagement with the bottom of theclamping arm. After that, the fastener screw is finally tightened. As aresult, the threaded sleeve defines the position of the clamping arm sothat the pocket obtains a correct height relative to a self-wedgingcutting insert.

OBJECTS OF THE INVENTION

One object of the present invention is to provide a rigid toolpreferably for thin holders and thin cutting inserts.

Another object of the present invention is to provide a tool in whichthe clamp is not distorted.

Still another object of the present invention is to provide a tool inwhich the clamping arm is protected from plastic deformation.

These and other objects have been achieved by a tool as defined in theappended claims with reference to the drawings.

SUMMARY OF THE INVENTION

The present invention relates to a toolholder for holding a cuttinginsert. The toolholder comprises a base and a clamping arm connected tothe base. The base and the clamping arm form therebetween a pocket andslot. The pocket has opposing surfaces and is open at a front endthereof for receiving a cutting insert. The slot extends rearwardly froma rear end of the pocket. The clamping arm is elastically biased to aposition wherein the surfaces of the pocket are spaced apart. Afastening screw is provided for displacing the clamping arm toward thebase against the elastic bias for clamping a cutting insert between thesurfaces of the pocket. A non-adjustable spacer of fixed height isdisposed in the slot for limiting an extent of movement of the clampingarm toward the base.

The invention also pertains to a method of attaching the cutting insertto the tool holder. In the method, after the cutting insert has beeninserted loosely into the pocket, the fastening screw is rotated todisplace the clamping arm toward the base to create an initiallytightened contact between the cutting insert and the pocket surfaces,with the clamping arm being in non-engagement with a spacer disposed inthe slot to form a gap therewith. Then, the fastening screw is furtherrotated to finally tighten the contact and cause the clamping arm to beelastically deformed in the region of the gap, whereby the gap is closedand the spacer prevents further displacement of the clamping arm towardthe base.

DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawing in which like numeralsdesignate like elements, and in which:

FIG. 1 shows a tool according to the present invention, in a side view;

FIG. 2 shows the tool in a top view;

FIG. 3A shows the tool in another side view, partly sectioned in an openposition;

FIG. 3B shows the tool in a clamped position;

FIG. 4 shows a holder in a front view;

FIG. 5 shows a cutting insert to be used in the tool in a front view;and

FIG. 6 shows an alternative embodiment of a tool according to thepresent invention in a side view.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1-5, there is shown a tool 10, including aholder 11 and a cutting insert 12. The holder 11 is of the type where abase of the body forms a lower side 19 of the pocket 14. A clamping arm13, integrated with the holder, constitutes an upper side 15 of theinsert pocket 14. The arm is movable in cantilever fashion about aportion of the holder which defines a pivot 27 by means of a fasteningscrew 17, the movement being accommodated by a slot 16. The slot 16connects with a rear end of the cutting insert pocket. The slot extendsin the longitudinal direction of the cutting insert for an appropriatedistance beyond the screw 17. The screw 17 as seen in FIG. 3A isprovided substantially in the middle of the elongated slot 16. The screw17 fits into a threaded boring 45 which has a center axis CL. Anabutment surface 34 is provided in connection with the lower border lineof the slot 16, wherein the surface 34 constitutes a stop for thecutting insert in its longitudinal direction. The slot 16 extendsrearwardly from the surface 34.

The upper side 15 has a generally convex V-shaped cross-section forminga projection with flanks 15 a, 15 b converging towards the cuttinginsert. The flanks form an obtuse, internal angle a with each other,which lies in the interval 120° to 160°. A clearance surface is providedbetween the flanks (i.e., at the peak of the V-shape) in order to avoida central contact with the cutting insert. The arm is intended to clampthe cutting insert against the lower side 19 of the cutting insertpocket.

The lower side 19 is formed with a number of separate, identical grooves26, which in cross section describe a substantially trapezoidal path.The grooves are elongated and extend along the entire lower side 19 in afront-to-rear direction. The direction F, which is the feed directionwhen the tool is used as a parting tool, and the direction L, which isthe feed direction when the tool is used as a tool for longitudinalturning, are shown in FIG. 2. The angle a between the directions F and Lcan be 90°±15°. The groove 26 further has two flanks which connect tothe groove bottom via a sharp or rounded transition. The flanks form anacute angle with each other,

The cutting insert 12 comprises an upper surface 18 and a lower surface29 interconnected by side surfaces 20, 21, 22, 23, wherein the lines ofintersection between the side surfaces 22, 23 and the upper surface 18form cutting edges 24, 25. The cutting insert is preferably somewhatwider than the cutting insert pocket, for the sake of clearance. Thelength of the insert edge 24 is shorter than the height of the cuttinginsert as measured between upper and lower surfaces 18, 29. The uppersurface has a slot formed by two flanks 18 a, 18 b which convergetowards the lower surface 29 with an external single substantiallycorresponding to the above-mentioned internal angle α. The lower side isformed by a number of separate, substantially, identical ridges 30. Theridges form a substantially sinusoidal curve. The ridges are elongatedand extend along the entire lower side 29 in a front-to-rear direction.The ridge 30 has two flanks 30 a, 30 b which connect to a bottom 31. Theflanks form an acute angle with each other.

As described thus far, the apparatus corresponds to the prior art. Thetool according to the present invention however, further comprises anexternally threaded sleeve or set screw 40, an annular member or aspacer 41 and a washer 42, all being substantially symmetricallypositioned relative to the axis of the screw 17. The axis of the screw17 is substantially perpendicular to the slot 16. The set screw 40includes a cylindrical portion 40 a which threads into a complementary,threaded boring 44 in the holder. A flange 43 is disposed at a free endof the cylindrical portion 40 a. The set screw flange 43 and a shoulder40 b of the boring cooperate to define the maximum height of the insertpocket.

The spacer 41 is preferably a metallic circular ring of fixed heightwhich is positioned in the slot 16 coaxially around the set screw 40.The spacer 41 is positioned where the clamp means 13 bends the mostduring clamping of the insert, i.e., in the middle of the slot 16. Themaximum height of the slot 16 is depicted by E. The thickness of thespacer 41 is depicted by T, which is a distance S thinner than theheight E. The distance or gap S allows the arm 13 to deform elasticallyto a certain extent during final tightening of the screw 17, i.e., thegap S is provided to be closed during tightening of the screw 17 asshown in FIG. 3B.

The provision of the washer 42 allows the threaded shank of the screw 17to come into threaded engagement with the boring in the holder, but willstop the head of the screw 17 from reaching the set screw 40 duringtightening. In order to avoid confusion of an operator in distinguishingthe washer 42 from the spacer 41, the internal diameter of the spacer 41is larger than the internal diameter of the washer 42.

Assembly of the tool according to the present invention is done asfollows, preferably at the tool manufacturing site. The spacer 41 isaligned with the center axis CL within the slot 16 on the slot floor 46.The spacer is not supposed to project from the slot outside of the tooland it will not extend to or interfere with the insert pocket. Then theset screw 40 is screwed into the boring 44 through the spacer, using aspecial turning tool which engages the flange 43. When the set screwflange 43 abuts the annular shoulder 40 b in the arm 13, the arm will beforced to close the slot 16 somewhat. A conventional reference insert,i.e., a non-working gauging insert of the type “Go/No go” for sizing apocket height is inserted in the pocket, and the set screw 40 istightened until only the “Go” part of the insert can be inserted but notthe “No go” part. The upper position of the arm 13, i.e., the maximumheight E, is thus determined. If desired, the set screw could beprovided with a thread lock means to avoid accidental displacementthereof. Then the fastening screw 17 is inserted through the washer 42and inserted into the boring 45 and tightened somewhat.

After the thus-assembled unit is shipped to a purchaser, an operator canuntighten the screw 17, whereupon the pocket achieves its maximumpermitted height, i.e., the height of the cutting insert pocket 14 isincreased by the release of stored elastic energy in the arm 13 untilthe shoulder 40 b abuts the flange 43. Therefore, the shoulder 40 b andthe flange 43 form mutually engageable stop surfaces. Thus, excessiveopening of the slot producing plastic deformation of the clamping arm,is avoided, even as a working cutting insert is inserted into the pocketsuch that associated ridges 30 and grooves 26 come into engagement witheach other. When the insert pocket is at its maximum allowed height, theinsert cannot be inserted unless the V-shaped upper side 15 of theinsert pocket is aligned with the slot formed in the upper surface ofthe insert. Therefore, in such an instance, the insert can only beinserted in a proper lateral relationship with the serrations 26 of thelower surface of the pocket. As the cutting insert is inserted, it isguided by said engagement, until the insert inner edge surface 23 abutsagainst the abutment surface 34. Subsequently the screw 17 can bescrewed-down such that the flanks of the arm 13 abut against associatedflanks on the cutting insert, whereby the ridges are firmly pressedagainst the grooves. To avoid overclamping of the arm 13 resulting ininsert breakage or permanent distortion of the arm the calibrated spacer41 is used. That is, when the screw 17 is finally tightened and theinsert is firmly clamped, the screw may be further tightened only untilthere is no longer a gap S between the arm 13 and the spacer 41. In thatposition the ceiling 47 of the slot abuts the spacer and thus preventsfurther tightening of the screw. When the insert is to be replaced orindexed, only the screw 17 is untightened such that the gap S willreappear at the position shown in FIG. 3.

In FIG. 6 there is shown an alternative embodiment of a tool 10′according to the present invention, wherein a separate plate 13′ isprovided and is fastened on a holder 11′ of the tool. In this case thepivot 27′ is constituted by two abutment lines or surfaces 48, 49. Thecutting insert is clamped in the same way as described above except thatthere is no stored elastic energy in the clamping arm. The elasticenergy is then preferably provided by a separate spring such as a washer50 which is disposed radially outside of the spacer and in surroundingrelationship thereto. The spring washer is compressed when the insert isclamped and is operable to raise the arm 13 when the fastening screw isloosened.

It should be understood that the sleeve 40 in some cases could beomitted, for example if the arm is very stable. Also if the head of thescrew 17 is of larger diameter than shown, then the washer 42 can beomitted. Furthermore, the spacer means 41 for restricting overclampingof the clamp arm 13 could alternatively be integrated with either theclamp arm 13 or the tool holder body 11 at a location close to the screwmeans, instead of being separate therefrom. When the fastening screw 17is loose, a gap would be created between the spacer and either the arm13 or the base of the body 11.

The tool according to the present invention provides the advantages ofoptimal looking force on the insert thereby avoiding breakage orpermanent distortion of the clamp, and trouble-free locking mechanismalso if the locking screw is over-torqued.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A toolholder for holding a cutting insert,comprising: a base and a clamping arm connected to the base, the baseand the clamping arm forming therebetween a pocket and a slot, thepocket having opposing surfaces and being open at a front end thereoffor receiving a cutting insert, the pocket having a rear abutmentsurface to be contacted by a cutting insert, the slot extendingrearwardly from the rear abutment surface, the clamping arm beingelastically biased in a direction wherein the surfaces of the pocket areurged away from one another; a fastening screw for displacing theclamping arm toward the base against the elastic bias for clamping acutting insert between the surface of the pocket; a non-adjustablespacer of constant fixed height disposed in the slot for limiting anextent of movement of the clamping arm toward the base, the clamping armbeing out of engagement with the spacer when the surfaces of the pocketare spaced apart sufficiently to afford insertion or removal of acutting insert.
 2. The toolholder according to claim 1 wherein thespacer is located adjacent a location of greatest bending of theclamping arm during an insert-clamping operation.
 3. The toolholderaccording to claim 1 wherein the spacer is situated substantially midwayalong a length of the slot.
 4. The toolholder according to claim 1wherein the spacer is separable from both the base and the clamping arm.5. The toolholder according to claim 1 wherein the fastening screwextends through the slot from the clamping arm to the base, the spacersurrounding the fastening screw.
 6. The toolholder according to claim 5wherein the spacer is ring-shaped.
 7. The toolholder according to claim5 wherein the fastening screw extends perpendicular to the slot.
 8. Thetoolholder according to claim 1 wherein the base and the clamping armare of one-piece integral construction.
 9. The toolholder according toclaim 1 wherein the clamping arm is separable from the base, and aspring is provided for elastically biasing the clamping arm.
 10. Thetoolholder according to claim 1 further including a cutting insertcontacting the rear abutment surface.